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Chapter: Environmental Engineering - Water Distribution And Supply To Buildings

Distribution System Appurtenances

The SPU water distribution system includes a number of smaller appurtenances, such as valves, hydrants, service lines, and meters. The paragraphs below summarize SPU's inventory and replacement approach for each class of appurtenance.

DISTRIBUTION SYSTEM APPURTENANCES

 

The SPU water distribution system includes a number of smaller appurtenances, such as valves, hydrants, service lines, and meters. The paragraphs below summarize SPU's inventory and replacement approach for each class of appurtenance. Distribution System Valves. SPU's water distribution system includes more than 21,000 valves. More than 16,600 valves control the flow of water through the distribution system, but other valves regulate pressure, bypass other facilities, or allow air to escape the system. Most valves within the distribution system are gate valves. The only significant modification to SPU's valves planned since the 2001 Water System

 

Plan will be the valve chamber replacement program that will replace existing chamber tops and access maintenance holes with larger diameter tops and new access ladders. This program will provide SPU maintenance staff with safer valve chamber access and meet industry safety standards. SPU has an ongoing program to replace line valves when they fail beyond repair, when no replacement parts are available, or where the cost of repair exceeds the cost of replacement. The determination of when a valve should be replaced instead of repaired is based on consultation among SPU staff experts.Distribution System Service Connections. SPU maintains approximately 180,000 service connections, 80 percent of which are -inch diameter pipes. Almost 70 percent of service connections are copper, and 20 percent are plastic. The remaining 10 percent are galvanized iron, ductile iron, and other materials.

 

The most significant change to SPU's service connections since 2001 is the initiation of a program to proactively replace noncopper service connections with copper connections. This program is intended to reduce the high leakage and failure rate ofnon-copper service connections

and is expected to be complete by 2015. The most appropriate assessment of the condition of SPU's service connections is their leakage rate.  In 2005, SPU's leakage rate from its service connections was approximately 2.8 leaks per 1,000 service connections.  This is lower than the IWA's target leakage rate of 3.75 leaks per 1,000 service connections for a well-run utility. The current volume of leakage from SPU's service connections is estimated between 2.8 to 4.0

million gallons per day (mgd), or between 15 to 22 gallons per day per service connection.

IWA's target leakage volume is approximately 15 gallons per day per service connection. SPU's non-copper service connections have leakage rates that are greater than 5 leaks per 1,000 service connections. By proactively replacing these non-copper service connections with copper connections, SPU expects to reduce the service connection leakage rate down to 1.5 leaks per 1,000 service connections, well below the IWA target. For all other copper services, SPU's replacement program is a 'run-to-failure' strategy, since the impacts of a failed copper service are typically minor, and the services can be quickly replaced. Distribution System Meters. Each service line is fitted with water meters used to determine customer charges. Most of the meters (87 percent) are for residential customers, and the remaining 13 percent are for commercial customers. Nearly 92 percent of SPU meters are small (3/4-inch and 1-inch). Since the 2001 Water System Plan, the most significant change to distribution meters, other than routine meter replacements and repairs, has been the installation of radio frequency modules on difficult-to-read meters in the downtown area. Also, radio frequency modules were installed in 2005 at a group of multifamily residential meters to pilot-test a new technology to collect readings from a single pole-mounted collector.


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